At present, the Institute of Electrical and Electronics Engineers (IEEE) 802.11u standard group mainly study the functions of interworking between Wireless Local Area Network (WLAN) and External Networks. The purpose of interworking between WLAN and external networks is to obtain information from external networks to help terminals with network selection, Quality of Service (QOS) mapping, and Emergency Alert System (EAS) support.
The emergency alert service provides a user with notification of an emergency alert event to allow the user to obtain the alert information. The interworking with external systems in the 802.11u involves support for the EAS. This service involves transmitting emergency alert information from an AP STA to a non-AP STA by using the Generic Advertisement Services (GAS) protocol. The AP STA sends a beacon frame that contains a one-bit EAS notification indication field (that is, EASN field) to the non-AP STA to indicate whether an emergency alert occurs. If the AP STA on an 802.11u infrastructure network receives emergency alert information from an external network, the AP STA sets the EASN field of the interworking element in the beacon frame to 1 to inform the non-AP STA of an emergency alert. When the non-AP STA receives a beacon frame from the AP STA and finds that an emergency alert occurs, the non-AP STA obtains the emergency alert information from the AP STA by using the GAS protocol and informs the user of the information.
FIG. 1 shows a processing flowchart of an AP STA for the EAS by using existing technologies. The flowchart includes:
Step 101: During initialization after power-on, the AP STA sets the value of the EASN field in the beacon frame to 0.
In the existing technologies, one binary bit is set in the EASN field. This bit serves as the alert status indication field. The value 1 indicates that an emergency alert occurs. The value 0 indicates that no emergency alert occurs.
Step 102: A judgment is made about whether emergency alert information is received. If emergency alert information is received, the process proceeds to step 103; if not, the process returns to step 102.
Step 103: A judgment is made about whether an emergency alert occurs. If an emergency alert occurs, the process proceeds to step 104; if not, the process proceeds to step 108.
Step 104: The information about the emergency alert is saved.
Step 105: A judgment is made about whether the EASN field in the beacon frame is set to 0. If so, the process proceeds to step 106; if not, the process proceeds to step 107.
Step 106: The EASN field in the beacon frame is set to 1, indicating that an emergency alert occurs. The process proceeds to step 111.
Step 107: The value of the EASN field in the beacon frame remains unchanged. The process proceeds to step 111.
Step 108: A judgment is made about whether the emergency alert is cleared. If an emergency alert occurs, the process proceeds to step 109; if not, the process proceeds to step 110.
Step 109: The EASN field in the beacon frame is set to 0, indicating that no emergency alert occurs. The process proceeds to step 111.
Step 110: The value of the EASN field in the beacon frame remains unchanged. The process proceeds to step 111.
Step 111: The beacon frame is sent to the non-AP STA.
FIG. 2 is a flowchart of a non-AP STA for the EAS by using existing technologies. The flowchart includes:
Step 201: After power-on, the non-AP STA sets the value of the EASN field in the beacon frame to 0.
Step 202: A beacon frame is received from the AP STA to obtain the value of the EASN field.
Step 203: A judgment is made about whether the value of the EASN field is 1. If so, the process proceeds to step 204; if not, the process proceeds to step 202.
Step 204: The non-AP STA finds that the value of the EASN field is 1, which indicates that an emergency alert occurs. The non-AP STA obtains the emergency alert information from the AP STA by using the GAS protocol.
Step 205: The non-AP STA shows the user the current emergency alert information.
During research and practice of the existing technologies, the following problems are unveiled:
In existing technologies, one binary bit in the EASN field is adapted to indicate whether an emergency alert occurs. When the contents of a same emergency alert are updated or different emergency alerts occur continuously, the AP STA cannot notify these changes to the non-AP STA in a timely manner so that the non-AP STA performs timely processing. If the non-AP STA wants to obtain continuously changing emergency alert information, the non-AP STA needs to periodically obtain the emergency alert information from the AP STA. Therefore, the system efficiency is greatly affected.
Therefore, the method for the EAS by using the existing technologies cannot help handle changes to emergency alerts in a timely and efficient manner.